Apparatus for communication systems



N. F. AGNEW APPARATUS FOR COMMUNICATION SYSTEMS Feb. 10, 1942. 2,272,786

Filed May 9, 1941 Telephone Jez . INV TOR Nor BY HIS ATTIORNEY Agnew Patented Feb. 10, 1942 ATENT OFFICE APPARATUS FOR COMBIUNICATION SYSTEMS of Pennsylvania Application May 9, 1941, Serial No. 392,709

Claims.

My invention relates to apparatus for communication systems, and more particularly to calling apparatus for telephone systems. The invention finds peculiar use in communication systems for railways, but it is not, however, limited to such use and may be effectively employed in other communication systems for providing an indication at a central station in response to a calling current sent from a field station.

In communication systems where a central ofiice station is connected to a plurality of outlying stations by a common transmitting channel, calling means is usually provided by which the central station operator can call any one of the outlying stations to initiate communication, and a person at any one of the outlying stations can call in to the central station to initiate communication. Such calling means must be selective not only as to the individual stations of the system but in many cases it must be unique as to the associated system because the transmitting channel may be used by several control and communication systems. For example, in communication systems for railways a single transmitting channel in the form of a pair of line wires may be used for a train dispatchers telephone circuit, a duplex telegraph circuit, one side of a phantom telephone circuit and as a centralized traffic control line circuit. In each of such circuits the current used is peculiar to the system. For example, in the centralized traffic control system codes of the time code type are used and an operator at the central office station governs the position of signals, switches and other traffic governing devices at different field stations by sending codes selective as to the field stations and to the control to be effected at the selected station, and in addition to such control codes, telephone communication is usually provided between the field stations and the central ofi'ice station, so that train crews, maintainers and other persons may receive verbal orders from the central station operator or dispatcher. Ordinarily in such communication system for railways the dispatchers telephone circuit and the centralized trafiic control circuit terminate at the same central office.

In such facilities for railways, as Well as for communication systems in general, it is advantageous to have means available for calling both ways on the transmitting line circuit. In a dispatchers telephone system, a call selector at each way station of the system is usually bridged across the line wires so that each station is the several different line circuits.

normally in a condition of being raised by the dispatcher when a corresponding calling key at the dispatchers office is released to send out a preselected series of electrical impulses, the selector at the respective way station operating to close a local call bell circuit in response to the respective series of impulses. In a preferred form of centralized trafilc control system, a code step is provided which may be used for calling from the central office station to any one of the field stations. For calling the central station from an outlying station in such systems for railways, it has been proposed to provide a loud speaker at the central station normally in circuit. lihis is not satisfactory because usually several line circuits terminate at the same central ofiice and a loud speaker for each line circuit becomes very confusing and annoying. Furthermore, the central station operator ordinarily uses the same telephone set to plug into any one of Again, it is not satisfactory to provide each way station or field station with a magneto or howler to call the central station operator because of the confusion and the extreme noise that may be produced by such devices.

In view of these conditions, a feature of my invention is the provision of novel and improved calling apparatus for communication systems.

Another feature of my invention is the provision in systems of the type here involved of novel calling means wherewith a voice operated relay at an office station governs the ringing of a call bell or the display of a call indication in response to a person speaking into a telephone transmitter at any one of the different field stations. 1

Again, a feature of my invention is the provision in calling apparatus of the type here contemplated wherewith an answer back is provided so that a person calling from a field station can hear the ringing of the office station call bell.

Still another feature of my invention is the provision of novel calling means for communication systems wherewith special calling equipment at each field station is avoided.

Again, a feature of my invention is the provision of novel calling means of excellent selectivity and which is unaffected when the line circuit is used for other forms of signaling such as, for example, duplex telegraph and centralized traffic control.

Another feature of my invention is the provision in communication systems of novel calling means which is economical and requires a minimum of equipment.

Other objects and advantages of my invention will appear as the specification progresses.

The above recited features, objects and advantages of my invention are attained by providing at the office station a selective receiving circuit, an electron tube, a relay, 3. call bell or indicator and an answer back circuit, together with proper sources of current. The receiving circuit is normally bridged across the line circuit and a filter interposed therein is proportioned to pass only frequencies of a preselected band, such as a preselected band of voice frequencies. The electron tube is preferably of the controlled ionization type and the relay together with a proper source of current are connected across the anode and cathode of the tube to energize the relay by the current passed by the tube when the tube is ionized, the voltage of the current source being, however, normally insufficient to start ionization but sufficient to cause the tube to break down when a preselected control electromotive force is applied to the control element or grid of the tube. The control element of the tube is provided with a circuit coupled to the receiving circuit and the positive half cycle of the energy passed by the filter serves to drive the grid in the positive direction and cause ionization of the tube. The arrangement is such that ionization of the tube continues only as long as a control electromotive force is present, that is, the tube is deionized when the control electromotive force ceases. The relay on picking up completes operating circuit for the call bell or indicator with the result that such device is operated as long as the tube is ionized.

The operating circuit for the bell is coupled to the line circuit by an answer back circuit which includes a condenser and a contact of the relay with the result that when the relay is energized and the bell is operated, energy having oscillations within the voice frequency range is applied across the line circuit and causes a tone in the telephone receiver at the calling station as an answer back to the person calling. The several parts can be proportioned so that a sufficient portion of the answer back energy is passed by the filter of the receiving circuit to the control element of the electron tube to provide the necessary control electromotive force by regeneration with the result that ionzation of the tub and ringing of the bell once initiated by a voice current are continued after such voice current ceases. I provide a push button in the bell operating circuit by which the central station operator can acknowledge the ringing of the call bell and stop its operation. Again, the parts can be so proportioned that the answer back energy is not passed by the receiving circuit to the control element of the tube or at least an insufiicient amount is passed to eiiect regeneration with the result that the deionization oi the tube is effected and the ringing of the call bell is automatically stopped when the voice current ceases. The connection of the receiving circuit to the line circuit includes a switching key at which the operator plugs in his loud speaker or telephone set to the line circuit, the arrangement being such that the receiving circuit is disconnected from the line circuit when the central oflice station loud speaker or telephone set is plugged into the line circuit.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic view showing one form of apparatus embodying my invention.

Referring to the drawing, the reference characters Y and Z designate line wires which extend between two or more spaced locations to provide a transmitting channel between such locations. For example, line wires Y and Z may be two line wires extending between two terminal stations of a railway and may be used in a dispatchers telephone circuit, may be simplexed in the usual manner for a telegraph circuit, may serve as one side of a phantom telephone circuit and may be employed as the line circuit of a centralized traffic control system. It is to be understood, of course, that my invention is not limited to a pair of line wires included in several such facilities and line wires Y and Z may be used for a telephone communication system only. In order to not unduly complicate the drawing, and to aid in the understanding of my invention, line wires Y and Z are shown as used for a telephone system only and in which system a central ofiice station indicated at CS and one field station indicated at F8 are disclosed, it being understood than any number of field stations similar to the field station FS may be included in the system.

At field station FS a telephone set including a transmitter 2 and a receiver 3 is connected in the usual manner across the line wires Y and Z over wires 4 and 5, At the central ofiice station CS a receiving circuit is normally bridged across the line wires Y and Z, such circuit being traced from line wire Y over wire I, normally closed contact 9 of a switching key to be later referred to, wire 2? primary winding 6 of a transformer Ti, condenser 5, wire 32, another normally closed contact it of the switching key and wire 8 to line wire Z. Primary Winding 6 of transformer TI and condenser 5 form a filter which is proportioned to pass a preselected band of frequencies. For example, the filter may be proportioned to pass a voice frequency band of 1,000 to 2,000 cycles per second. It is to be pointed out that the invention is not limited to such frequency band and the pass band of the filter may include the full voice frequency range or it may be made narrow to include a single voice frequency.

The central station CS is provided with an electron tube ET of the controlled ionization type, and preferably tube ET is of the cold cathode type. Tube ET is provided with an anode circuit which in the present embodiment of the invention includes a source of alternating current and a relay. To be explicit, this anode circuit can b traced from terminal BX of secondary winding 26 of a transformer T2 to whose primary winding 2! is connected a source of alternating current such as a generator not shown, resistor 22, anode l l of tube ET, tube space to cathode l3, winding of a relay RI and to the other terminal CX of the secondary winding 20 of transformer T2. A condenser M is preferably connected across the winding of relay RI. Tube ET is provided with a control or grid circuit that is coupled to the receiving circuit, such control circuit being traced from control element or grid l5 of tube ET over condenser 56, resistor ll, secondary winding ill of transformer TI, mid terminal of a resistor l9 connected across secondary winding 20 of transformer T2, and thence to the cathode 13 of the tube through the winding of relay Rl and condenser I4 in multiple. The voltage of secondary winding 29 of transformer T2 and the biasing voltage of control element I5 of thetube as efiected from resistor I9 are such that normally the tube is not ionized and no current fiows in the anode circuit with the result that relay RI is normally deenergized and released. When an electromotive force is applied to the control element I5 of tube ET to drive that element in the positive direction a predetermined value the voltage of secondary winding of transformer T2 breaks down the tube and positive h'alf cycles of current flow through the tube to energize the relay RI. This condition persists as long as such electromotive force is applied to the control element I5, but once such electromotive force is stopped, then the next negative half cycle of the alternating current serves to deionize the tube and restore it to its normal condition.

At the central station CS a call bell C3 is provided with an operating circuit including battery 22, front contact 23 of relay RI, back contact 22 of the bell, operating winding 25 of the bell, and push button 26 back to battery 22. Thus the bell C3 is operated when the relay RI is energized and picked up.

This operating circuit for bell C3 is coupled to the lin wires to provide answer back energy. Such answer back circuit can be traced from the right-hand terminal of bell winding 25 as viewed in the drawing, over front contact 28 of relay RI, condenser 29, wire 32, contact II! of the switching key, wire 8 to line wire Z, any telephone set that may be connected between line wire Z and line wire Y, wire I, contact 9 of the switching key, Wire 21, push button 26 and to the left-hand terminal of bell winding 25. In multiple with the winding 25 is a path including back contact 22 of the bell, front contact 23 of relay RI and battery 22. It is also to be noted that the filter including primary winding 6 of transformer TI and condenser 5 is connected to this answer back circuit in shunt with the line wires Y and Z. The function of this answer back circuit will shortly appear.

When a person at field station FS desires to call the central office station, the receiver 3 is removed from the hook and a suitable word or phras is spoken into the transmitter 2. The voice or telephone current thus supplied to the line wires Y and Z causes current of the pass band of the filter including condenser 5 and winding 6 to fiow in the receiving circuit. Transformer TI is proportioned so that a relatively high voltage low amperage electromotive force of the frequency passed by the filter is induced in secondary winding it of the transformer and which winding is included in the control circuit of tube ET. Each positive half cycle of such electromotive force drives the control element I5 in the positive direction sufficient to initiate ionization of the tube. With tube ET ionized, the positive half cycles of the alternating current from transformer T2 are passed by the tube and the relay RI is energized and picked up, the picking up of relay RI being delayed untilcondenser I2- is fully charged. Relay RI on picking up to close front contact 23 completes the operating circuit of bell C3 and the bell rings in the usual manner. The parts are so proportioned that the interruptions of the operating circuit at back contact 24 of the bell occur at a rate or frequency within the voice frequency range, or at least at a rate that produces harmonic oscillations within the voice frequency range. Such oscillations cause energy of a corresponding frequency to be applied to the line wires Y and Z by the answer back circuit with the result that a corresponding tone is produced in the receiver 3 at field station FS as an answer back to the person calling. That is to say, this tone thus produced in the receiver 3 at the field station serves to indicate to the person calling that the call bell at the central station is operating.

It is clear that ionization of tube ET is initiated by each positive half cycle of the telephone current passed by the filter of the receiving circuit but that the tube ET is deionized immediately following the stopping of such telephone current by the negative half cycles of the alternating current supplied by transformer T2, unless the regenerative action of the answer back energy supplied to the line circuit due to the operation of hell C3 is such as to continue ionization of the tube. I have found that by proper proportioning of the parts, the tube ET is deionized and relay RI released to stop the ringing of the bell when the telephone current ceases, and that the parts can also be properly proportioned so that a sufficient amount of the answer back energy will be passed by the filter of the receiving circuit to create in the control circuit of the tube energy that continues the ionization of the tube, with the result that ionization of the tube and operation of the bell once initiated by a voice frequency current such operation is continued indefinitely after the voice frequency current ceases, or until stopped by some other means. In this latter condition the call can be acknowledged and the operation stopped by the central oifice station operator actuating the push button 26 in the operating circuit of the bell circuit.

Upon receipt of such a call from a field station the central station operator would connect the telephone set conventionally indicated at TS to the line wires Y and Z by plugging in the telephone set at the switching key which completes the connection for the telephone set at contacts 30 and 3|. The calling apparatus, that is the receiving circuit for the calling apparatus, is disconnected at contacts 9 and I0 of the switching key when the telephone set TS is connected to the line circuit. When the operator has connected his telephone set to the line circuit then I telephone communication between the operator and the person at the field station is effected in the usual manner. At the termination of such telephone communication, the telephone set of the central ofiice would be disconnected from the line with the result that the calling apparatus is again connected thereto.

I have found that such calling apparatus is highly selective and is non-responsive to telegraph current, or centralized traffic control codes or to the usual selective codes sent out from the central office station to call a field station. Furthermore, the filter of the receiving circuit prevents shock energization created by a single impulse on the line circuit from initiating ionization of the tube, and even in the event ionization of the tube is effected, such condition must persist for a predetermined period of time sufficient to charge condenser It before relay RI is picked up to start operation of the call bell.

In addition to being highly selective, such calling apparatus has the advantage that special calling devices at each field station are avoided and no energy is required to maintain the calling apparatus in an active condition.

It is to be pointed out that although I have shown the anode circuit of tube ET as provided with a source of alternating current, it is to be understood that a source of direct current may be used and a reactor device associated with the anode circuit for causing deionization of the tube subsequent to the removal of the control electromotive force from the control element of the tube.

Although I have herein shown and described but one form of apparatus for communication systems embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In apparatus for a communication system the combination comprising, a first and a second station effectively connected by a transmitting channel, telephone means at the first station capable of supplying to said channel a current containing voice frequencies, a receiving circuit including capacitance and inductance at the second station adapted to receive energy from said channel and adjusted to pass a given band of voice frequencies, an electron tube of the controlled ionization type and an electrcmagnet at said second station, means including a source of current to connect said electromagnet across the anode and cathode of said tube to energize the electromagnet when the tube is ionized but normally ineffective to cause ionization, a control circuit coupled to said receiving circuit and connected to the control element of said tube to initiate ionization of the tube in response to such voice frequency cuirent supplied to the transmitting channel at said first station, and a calling device controlled by said electromagnet.

2. In apparatus for a communication system the combination comprising, a first and a second station effectively connected by a transmitting channel, telephone means at the first station capable of supplying to said channel a current containing voice frequencies, a receiving circuit including capacitance and inductance at the second station adapted to receive energy from said channel and adjusted to pass a given band of the voice frequencies only, an electron tube of the controlled ionization type and a relay at said second station, means including a source of current to connect said relay across the anode and cathode of said tube to energize the relay when the tube is ionized but normally ineffective to cause ionization, a control circuit coupled to said receiving circuit and connected to the control element of said tube to initiate ionization of the tube in response to such voice frequency current supplied to the transmitting channel at said first station, a call bell, an operating circuit including a current source and a contact of said relay to operate said call bell when the relay is energized, and an answer back circuit including a :contact of said relay to .couple said operating circuit to said transmitting channel to apply to the transmitting channel energy having audible frequencies due to operation of the bell to create at the telephone means of the first station an answer back tone,

3. In apparatus for a communication system the combination comprising, a first and a second station effectively connected by a transmitting channel, telephone means at the first station capable of supplying to said channel a current containing voice frequencies, a receiving circuit including capacitance and inductance at the second station adapted to receive energy from said channel and adjusted to pass a given band of the voice frequencies only, an electron tube of the controlled ionization type and a relay at said second station, means including a source of current to connect said relay across the anode and cathode of said tube to energize the relay when the tube is ionized but normally ineffective to cause ionization, a control circuit coupled to said receiving circuit and connected to the control element of said tube to initiate ionization of the tube in response to said voice frequency current supplied to the transmitting channel at said first station, a call bell, an operating circuit including a current source and a contact of said relay to operate said call bell when the relay is energized, an answer back circuit including a contact of said relay and a condenser to couple said operating circuit to said transmitting channel to apply to the transmitting channel energy having frequencies within said given voice frequency band due to operation of the bell to create at the telephone means of the first station an answer back tone and to supply to said control circuit through the receiving circuit a regenerative electromotive force, and a manually operable switch interposed in said call bell operating circuit for opening of that circuit and stopping the calling operation.

4. In apparatus for a communication system using a line circuit extending between a first and a second station, the combination comprising, a telephone set at the first station adapted to supply to the line circuit a voice frequency current, a receiving circuit including a filter connected to the line circuit adjacent said second station and proportioned to pass a preselected band of voice frequencies only, an ionization type of electron tube and a relay at said second station, an anode circuit including a current source to connect said relay across the anode and cathode of said tube to pick up the relay when the tube is ionized but normally ineffective to cause ionization, a con trol circuit including a winding coupled to said receiving circuit connected to the control element of said tube to initiate ionization in response to said voice current supplied to the line circuit, a call bell connected to a current source over a front contact of the relay, and means to cause deionization of the tube when said voice current ceases.

5. In apparatus for a communication system using a line circuit extending between a first and a second station, the combination comprising, telephone means at the first station efiectively connected to said line circuit, a receiving circuit including a filter connected to the line circuit at said second station and proportioned to pass a preselected band of voice frequencies only, an ionization type of electron tube and a relay at said second station, a source of alternating current, an anode circuit including said alternating current source and said relay connected across the anode and cathode of said tube to energize said relay when the tube is ionized but normally ineffective to cause ionization, a control circuit including a winding coupled to said receiving circuit connected to the control element of said tube to cause ionization of the tube when a telephone current is supplied to the line circuit by the telephone means at said first station, a call bell operated over a circuit including a Cont ct of said relay, and another circuit including a contact of Said relay and a condenser to couple the operating circuit of said bell to said receiving circuit to effect regeneration and continue ionization of the tube once it is initiated by the telephone current.

6. In apparatus for a communication system using a pair of line wires extending between a field station and a central station, the combination comprising, telephone means at the field station effectively connected across said line wires for sending and receiving telephone currents; a transformer, an ionization type of electron tube, a relay, a source of alternating current and a call bell at said central station; a receiving circuit including a condenser and a primary winding of said transformer connected across said line wires and adjusted to pass a preselected band of voice frequencies, an anode circuit including said relay and alternating current source for said tube to energize the relay when the tube is ionized but normally ineffective to cause ionization of the tube, a grid circuit including a secondary winding of said transformer for said tube to apply an electromotive force to the grid of the tube which causes ionization of the tube each positive half cycle of the telephone current sent by said telephone means, an operating circuit including a contact of the relay to operate said call bell when the relay is energized, and an answer back circuit including a condenser and a contact of said relay to couple said operating circuit to said line wires to supply energy having oscillations within the voice frequency range to cause a tone in said telephone means when said bell is operated.

7. In apparatus for a communication system using a pair of line wires extending between a field station and a central station, the combination comprising, telephone means at the field station effectively connected across said line wires for sending and receiving telephone currents; a transformer, an ionization type of electron tube, a relay, a source of alternating current and a call bell at said central station; a receiving circuit including a condenser and a primary winding of said transformer connected across said line wires and adjusted to pass a preselected band of voice frequencies, an anode circuit including said relay and alternating current source for said tube to energize the relay when the tube is ionized but normally inefiective to cause ionization of the tube, a grid circuit including a secondary winding of said transformer for said tube to apply an electromotive force to the grid of the tube which causes ionization of the tube each positive half cycle of the telephone current sent by said telephone means, an operating circuit including a contact of the relay to operate said call bell when the relay is energized, and an answer back circuit including a condenser and a contact of said relay to couple said operating circuit to said line wires, and said answer back circuit effective when said bell is operated to supply energy having frequencies Within the voice frequency range to cause a tone at said field station telephone means and to continue ionization of said tube.

8. In apparatus for a communication system using a pair of line wires extending between a field station and a central station, the combination comprising, telephone means at the field station effectively connected across said line wires for sending and receiving telephone currents; a transformer, an. ionization type of electron tube, a relay, a source of alternating current and a call bell at said central station; a receiving circuit including a condenser and a primary winding of said transformer connected across said line wires and adjusted to pass a preselected band of voice frequencies, an anode circuit including said relay and alternating current source for said tube to energize the relay when the tube is ionized but normally ineffective to cause ionization of the tube, a grid circuit including a secondary winding of said transformer for said tube to apply an electromotive force to the grid of the tube which causes ionization of the tube each positive half cycle of the telephone current sent by said telephone means, an operating circuit including a contact of the relay to operate said call bell when the relay is energized, an answer back circuit including a condenser and a contact of said relay to couple said operating circuit to said line wires, said answer back circuit effective when said bell is operated to supply energy having frequencies within the voice frequency range to cause a tone at said field station telephone means and to continue ionization of said tube, and manually operabl switching means at said central station to disconnect said receiving circuit from the line wires and to connect a telephone set thereto.

9. In apparatus for a communication system using a pair of line wires extending between a field station and a central station, the combination comprising, telephone means at the field station adapted to be connected to said line wires for sending and. receiving telephone current; a transformer, a gas filled electron tube, a relay, an alternating current source and a call bell at the central station; a receiving circuit including a condenser and a primary winding of said transformer connected to said line wires and adjusted to pass a preselected band of voice frequencies, said tube provided with an anode circuit including said alternating current source and a winding of said relay in multiple with a condenser to energize the relay a given time interval after the tube is ionized, said tube provided with a grid circuit including a secondary winding of said transformer and a condenser to apply to the tube an electromotive force which initiates ionization each positive half cycle of a telephone current sent by said field station telephone means and. causes energization of said relay, an operating circuit including a front contact of said relay and a source of current for operating said bell, an answer back circuit including a condenser and a contact of said relay to couple said operating circuit to said line wires to cause a tone in said field station telephone means and to continue ionization of said tube due to the oscillation created by operation of said bell, and a manually operable switching means to disconnect said receiving circuit from said line wires and connect a telephone set thereto.

10. In apparatus for a communication system using a pair of line wires extending between a field station and a central station, the combination comprising, telephone means at the field station adapted to be connected to said line wires for sending and receiving telephone current; a gas filled electron tube, a relay, an alternating current source and a call bell at the central station; said tube provided with an anode circuit including said alternating current source and a winding of said relay in multiple with a condenser to energize the relay a given time interval after the tube is ionized, control circuit means including a filter connected to said line wires and coupled to the grid of said tube, said control circuit means adjusted to pass a preselected band of voice frequencies and effective to apply to the grid of said tube an e1ectromotive force which causes ionization of the tube in response to telephone current sent by said telephone means at the field station, an operating circuit including a contact of said relay when energized to operate said bell, an answer back circuit including a contact of said relay and a condenser to couple said operating circuit to said line wires to cause a tone in said field station telephone means and to continue ionization of said tube due to the oscillation created by operation of said bell, and manually operable means to render said answer back circuit inefiective.

NORMAN F. AGNEW. 

